JoystickBehaviour

using UnityEngine;
using UnityEngine.UI;
using System.Collections;


class Boundary {
    public Vector2 min = Vector2.zero;
    public Vector2 max = Vector2.zero;
}
[RequireComponent (typeof (Image))]

public class JoystickBehaviour : MonoBehaviour {

    [HideInInspector]
    public Vector2 output;                          //Joystick output in [-1, 1]

    public Vector2 deadZone = Vector2.zero;         //DeadZone for joystick
    public float maxDistance = 50;                  //MaxDistance from center
    public bool smooth = true;

    private Boundary bounds = new Boundary ();      //Boundary for graphics
    private RectTransform joystick;                 //Joystick transform
    private Vector3 defaultPosition;                //Default joystick position
    private int latchedFinger = -1;                 //Latched finger to avoid other fingers to steal joystick

    private bool canMove = false;
    private float distanceX = 0;
    private float distanceY = 0;

    private float canvasScale;

    void Start () {
        // Cache this component at startup instead of looking up every frame
        joystick = GetComponent <RectTransform> ();

        //Get canvas scale
        canvasScale = GetComponentInParent <Canvas> ().scaleFactor;

        //Default position is its start position
        defaultPosition = joystick.position;

        //Build joystick boundary to clamp joystick position
        bounds.min.x = joystick.position.x - maxDistance * canvasScale;
        bounds.max.x = joystick.position.x + maxDistance * canvasScale;
        bounds.min.y = joystick.position.y - maxDistance * canvasScale;
        bounds.max.y = joystick.position.y + maxDistance * canvasScale;
    }

    //Reset joystick to its default position
    void ResetPosition () {
        canMove = false;
        latchedFinger = -1;
        joystick.position = defaultPosition;
    }

    void Update () {
        //Graphics size /2 to calculate distance between input position and graphics position
        float sizeX = joystick.sizeDelta.x/2;
        float sizeY = joystick.sizeDelta.y/2;

        #if UNITY_EDITOR

        //Distance between joystick graphics snd mouse position
        distanceX = defaultPosition.x - Input.mousePosition.x;
        distanceY = defaultPosition.y - Input.mousePosition.y;

        //Calculate if mouse position is inside joystick graphics
        bool containsMousePosition = distanceX >= -sizeX &&
                                     distanceX <=  sizeX &&
                                     distanceY >= -sizeY &&
                                     distanceY <=  sizeY ;

        //Allow mouse move if it's inside joystick graphics
        if (Input.GetMouseButtonDown (0) && containsMousePosition)
            canMove = true;

        // Change the location of the joystick graphic to match where the mouse is and clamp its position
        if (Input.GetMouseButton (0) && canMove){
            Vector3 pos = joystick.position;
            pos.x = Mathf.Clamp (Input.mousePosition.x, bounds.min.x, bounds.max.x);
            pos.y = Mathf.Clamp (Input.mousePosition.y, bounds.min.y, bounds.max.y);
            joystick.position = pos;
        }

        // Reset position if click ended
        if (Input.GetMouseButtonUp (0))
            ResetPosition ();

        #else

        foreach (Touch touch in Input.touches){
            //Distance between joystick graphics snd touch position
            distanceX = defaultPosition.x - touch.position.x;
            distanceY = defaultPosition.y - touch.position.y;

            //Calculate if touch position is inside joystick graphics
            bool containsTouchPosition = distanceX >= -sizeX &&
                                         distanceX <=  sizeX &&
                                         distanceY >= -sizeY &&
                                         distanceY <=  sizeY ;

            //Allow touch move if it's inside joystick graphics & get latched finger id
            if (containsTouchPosition && touch.phase == TouchPhase.Began){
                latchedFinger = touch.fingerId;
                canMove = true;
            }

            // Change the location of the joystick graphic to match where the mouse is and clamp its position
            if (canMove && touch.fingerId == latchedFinger){
                Vector3 pos = joystick.position;
                pos.x = Mathf.Clamp (touch.position.x, bounds.min.x, bounds.max.x);
                pos.y = Mathf.Clamp (touch.position.y, bounds.min.y, bounds.max.y);
                joystick.position = pos;
            }

            // Reset position if touch ended
            if (touch.fingerId == latchedFinger && (touch.phase == TouchPhase.Ended || touch.phase == TouchPhase.Canceled))
                ResetPosition ();
        }

        #endif

        // Get a value between -1 and 1 based on the joystick graphic location
        output.x = (joystick.position.x - defaultPosition.x) / (maxDistance * canvasScale);
        output.y = (joystick.position.y - defaultPosition.y) / (maxDistance * canvasScale);

        // Adjust for dead zone
        var absoluteX = Mathf.Abs( output.x );
        var absoluteY = Mathf.Abs( output.y );

        if ( absoluteX < deadZone.x )
            output.x = 0;

        if ( absoluteY < deadZone.y )
            output.y = 0;

        //Smooth value, making it less sensible near center
        if ( smooth ) {
            output.y = output.y * output.y;
            output.x = output.x * output.x;
        }
    }
}